5. Troubleshooting
5.1 Troubleshooting for circuit-breaker proper (MCCB/ELCB)
Trouble
Cause
Closing impossible
Foreign matters to be removed
No resetting
To be reset once again
Abnormal operation
Resetting impossible
Wear due to trip endurance
Poor reset mechanism
(*) Resetting impossible
Tripping impossible
See below (*)
See below
Incessant use of voltage trip operation To be replaced with new one, Voltage trip to be replaced by electric operation
End of service life
To be replaced with new one
Poor adjustment
To be returned for repairing
Non-excitation of undervoltage coil Carelessness
To be excited
Resetting time has not elapsed
Wait until the bimetal is cooled down
Breakage by initial trouble
To be returned for repairing
switching spring
End of service life
To be replaced by new one
Fusion of contact due to excessive interruptive current
To be replaced by circuit-breaker with large breaking capacity
Broken handle
Breakage and/or fatigue of the
Excessive operation power
Handle to be replaced
Poor positional relationship between the external handle and the
Handle to be replaced
circuit-breaker
Revision of positional relationship
Excessive shock from exterior
To be replaced with new one
Poor electrification
OFF impossible
Countermeasure
Foreign matter in switching mechanism
Insulating material mingled between contacts
To be returned for repairing (with unremovable cover)
Corrosion by infiltrating rain water, etc.
To be replaced with new one
Fused conductive portion
To be replaced by new one with larger breaking capacity
Large consumption of contact
Excessive interrupting current
Short-circuit current cut off. End of service life
To be replaced with new one
Application of overcurrent
Breakage of rated changeover screw Excessive tightening torque (tighten with 3 to 4.5 kg-cm of torque)
Too high an ambient temperature
Troublesome operation
under normal load
Too high a temperature rise
Deviation of applied frequency (thermaladjustable electromagnetic type 800AF or higher)
Rating selection to be changed
Board hermetically closed
Ventilation
Loosened connection to terminal Retighten
Erroneous selection (frequency)
Load current strained with much high component
Distortion factor to be decreased by reactor
Rather small measurements by error of measuring instrument due to distorted current
To be measured correctly by a meter with true effective value, and correct selection of rating
Troublesome operation
Selection of rating to be changed
Correct the setting of rated current
display
Tightening forgotten of the changeover screw of rated current
Correct retightening of the rated current changeover screw with tightening torque: 3 to 4.5 kg-cm
MCCB
LED is on
Failure of rated current changeover portion
To be returned for repairing
Erroneous action while
Exothermic reaction due to repeated starting current
Erroneous selection
To be replaced by a unit with higher rating
starting
Too long a starting time
Erroneous selection
To be replaced by a unit with higher rating
Operating while in use
Short-circuit on line side
Too high a starting current
Electromagnetic setting to be change or the unit to be replaced by one with higher rating
Too high a starting rush current
Electromagnetic setting to be change or the unit to be replaced by one with higher rating
Transient current when changing delta connection to star one. Transient current due to reversible operation Electromagnetic setting to be change or the unit to be replaced by one with higher rating
Rush current at the time of instantaneous restart
Electromagnetic setting to be change or the unit to be replaced by one with higher rating
Rare short-circuit of motor
Motor to be repaired
Bimetal reset incomplete after instantaneous tripping
To be fully restored
Abnormal current running simultaneously with closing (short-circuit closing)
Circuit to be checked to remove the cause
Transmission was made with antenna of transceiver (5W or higher) Transceiver to be used at a distance at least 1 m from the electronic
closely mounted on the electronic MCCB and earth leakage breaker
MCCB
Shift from the short-circuit of another conductor
Cause to be removed To be replaced with new one
Accumulated dust
Cause to be removed To be replaced with new one
Cause to be removed To be replaced with new one
Fall of conductor on line side
Too high a temperature on
the terminal side
Temperature rise
To be replaced with circuit-breaker of suitable frequency
type
during starting
Poor tightening
Poor maintenance
Retighten
Contact heavily consumed
End of service life
To be replaced by new one
Increased contact resistance
Intrusion of rust and dust
Foreign matters to be removed
Too high a temperature on Complete electromagnetic type used in high frequency (400 Hz, for instance) Suitable frequency to be selected To be changed into thermal type.
the lateral side of the
Load current distorted containing much high frequency component
Distortion factor to be decreased by reactor Selection of rating to be changed
mould
Erroneous measurement dependent on feeling
To be measured with a measuring instrument
Loosened stud
Retighten
Poor contact between the conductive portion of stud and the body terminal
Reassemble the stud
Groove machining forgotten for reduction of eddy-current exothermic reaction of rear-connected type iron mount plate (400AF or higher)
Groove to be provided
Too high a rated current selected
To be replaced by a unit with lower rating
Exothermic reaction of the
tightened portion of stud
No operation with
tester
No operation
(electronic MCCB)
To be returned for repairing
Erroneous selection (temperature correction)
Electronic Overcurrent Too small a setting of rated current
Instantaneous action
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Foreign matter to be removed (with removable cover)
No tripping with over
Suitable frequency to be selected
Wrong frequency applied
current
Tripping of backup circuit-breaker
Too low a current for instanta-
Instantaneous electromagnetic switch to be lowered
neous tripping of backup breaker Raise the electromagnetic setting of backup breaker or change the rating
Overcurrent display LED does
not come on. Or, though it
comes on, it goes off sonner
than normal.
The battery of breaker tester has come at the end of its service life.
Battery to be replaced.
Overcurrent display LED comes
on and goes off after prescribed
time. But, no tripping.
Poor tripping mechanism
To be returned for repairing.
5.2 Troubleshooting for leakage operation portion
Trouble
Cause
Countermeasure
Operates simultaneously
Too long a wire and too large a ground electrostatic
with closing (such operation capacity causes the leak current to flow
Trouble- of leakage mechanism as
some
popping-out of the leakage
Normal operation due to leak current
action
display button)
Refer to 5.4
Operates during use
Leakage operation and the Poor lamp or its end of service life
Abnormal
Display button does not come out due to poor
like by test button, but no
operation
adjustment
display
Trouble in electronic circuit
No
Depressing the test button
No voltage applied
operation does not lead to operation
Poor continuity of contact
Rated sensitivity current to be changed, or
ELCB to be installed near load
Leak point to be repaired
To be replaced by new one
To be returned for repairing
To be replaced by new one
Apply specified voltage
Remove foreign matter on the contact
5.3 Troubleshooting of accessories
Trouble
Operation
disabled
NFM/NVM
(electric operation
device)
Continuous idling
One turn of idling
when closing
Closing disabled
UVT
(undervoltage tripping
No tripping even
device)
with no voltage
Cause
Countermeasure
Too low a capacity of the
Increase the diameter of the wire
wire of operational circuit
Voltage drop of
operational power supply Too low a capacity of the
Improve the operational power supply
operational power supply
Burnt resistor/motor
Regularize the wiring
Regular operational voltage to be applied
Self-sustaining auxiliary switch contact to be
used for automatic resetting
The contact for automatic resetting to be used
as that for alarm switch
Push button to be provided with interlock
Voltage tripping in OFF state or tripping by
undervoltage
OFF operation once to reset and ON operation
again
The circuit-breaker proper has automatically
cut off and tripped
Erroneous frequency or voltage applied
Power supply to be improved
No pulling
Too large a voltage drop Voltage to be improved
Trouble in circuit-breaker tripping mechanism
No tripping action
Coil burnt out
AL (alarm switch),
AX (auxiliary switch),
EAL (earth-leakage
Malfunction
alarm, switch),
MG (Insulation switch)
PAL (pre-alarm)
To be returned for repairing (replacement of
resister/motor)
Erroneous wiring
Erroneous voltage applied
Operation of ON and OFF circuits at the same
time or erroneous manipulation
Insufficient voltage
SHT (voltage tripping
device)
Excessive continuous
operation
To be returned for repairing
Operational voltage drop Power supply to be improved
Erroneous voltage applied Power supply to be improved
To be returned for repairing (replacement of
Continous excitation
coil, auxiliary contact to be provided for
of coil
protection from burning)
Continuous excitation under a voltage To be returned for repairing (replacement of
inferior to the operating voltage
coil), power supply to be improved
Poor auxiliary contact
for prevention of burning
Abnormal voltage applied
Poor contact due to overcurrent
Erroneous wiring
Erroneous wiring
when installing
To be returned for repairing (replacement of
coil, contact to be repaired)
To be returned for repairing (replacement of coil)
To be returned for repairing
Regular wiring to be made referring to the
name plate
To be returned for repairing (to be replaced
with that for microload)
Microload
Erroneous selection
Loosened attaching
screws
Insufficient tightening
To be returned for repairing (re-adjustment)
Vibration during transportation
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5.4 Analysis of unnecessary operation
Operation of ELCB by the causes on purpose, leak current, electrification, ground fault etc., is normal,
while operation by other causes such as surge and induction is unnecessary (called stray operation or
nuisance trip). It seems that quite a number of users have the preconception that earth leakage circuit
breakers are troublesome as they operate unreasonably. Therefore, unnecessary operation is analyzed
and selection of correct ELCB is stated in the following text.
5.4.1 Classification of ELCB operation
ELCB operation is classified as follows;
(1) Operation by leak current, electrification, ground
Normal
operation
fault etc.
Those
attributable
to ELCB
Operation
Unnecessary
operation
Those
attributable
to circuit and
others
(2) Fault of earth leakage circuit breaker
(3) Inadequate sensitivity current (too sensitive)
(4)
(5)
(6)
(7)
(8)
(9)
Operation by surge
Operation by circulation current
Operation by induction
Operation by wrong wire connection
Operation by inadequate earth
Operation by influence of at ground fault of shunt
circuit
(10) Operation by overload or short-circuit
(11) Operation by environment (vibration, impact etc.)
(12) Operation by carrier phone unit
(13) Operation by electromagnetic wave
(14) Operation by inverters
(15) Others (Operation of surge absorber etc.)
5.4.2 Detail of operation
(1) Normal operation
Operation of ELCB according to each purpose. Primary examples are shown below.
1 Deterioration of equipment insulation ...... This is often the case with water handling devices such
as washing machine and those subjected to high impact
such as press machine.
2 Deterioration of wire insulation ................ This is often the case with joints and terminals of temporarily installed electric lines.
3 Faulty work .............................................. Ground fault by damage or disconnection of cables during work.
4 Careless handling .................................... Electrification by wetting and ground fault by surge or
dropped foreign matter.
(2) Fault of ELCB
Failure caused by deterioration and corrosion of parts but fault of the leak detecting unit is rare. In
some cases, closing becomes unstable because of wear of the magnet or the switching mechanism.
Besides such fault, ELCB of low balancing characteristic tends to operation when the motor starts. It
is, therefore, necessary, to use ELCB made by reliable manufacturers.
(3) Inadequate sensitivity current
ELCB operates if the sensitivity current is too sensitive compared with normal leak current of the
circuit. This is a matter of selection.
In most cases, leak current from circuits is attributable to static capacity to ground of the wire. Of some
electric furnaces and sheath heaters, the insulation resistance comes down when cooled even if the
insulation resistance is enough at high temperature, and it takes time to find out the cause of ELCB
operation.
As to leak current from circuits, it must also be noted that ELCB is operated not only by leak current
under normal condition but also by transient leak current to ground at switching or at start-up. Transient
leakage at start-up is generated through static capacity to the frame of winding as potential distribution
of winding at start-up differs from that during operation.
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(4) Operation by surge
To surge by secondary transfer of inductive lightening of wires, non-operation test by lightening
impulse is set forth in JIS C-8371, and surge resistivity is ensured. Circuit of the lightening impulse non-operation test is shown at right.
Almost all NVs of Mitsubishi are provided with a
DPDC surge discrimination circuit for judging leak
current to ground by ground fault current and
surge so as to improve unnecessary operation
preventing function.
7kV
U
V C
R
W
Lightening impulse
voltage generator
C : 0.03µF
R : 0.1MΩ
Test circuit of lightening impulse non-operation
(5) Operation by loop circuit (circulation current)
In the parallel circuits connected at load side,
diverted current of each phase isn’t necessarily
equal between the right and the left branches. If
A phase is diverted into 11A and 9A, for example,
the difference of 1A is to be circulating in the
loop.
Parallel use of two ELCBs is therefore prohibitive as the circulation current causes operation
of the earth leakage circuit breaker.
(5) Operation by induction
Those with loop circuits are susceptible to induction. Taking a loop as a loop antenna, the primary winding of ZCT is to be connected with the
antenna, and induction is easily generated.
When a common earth wire is used, place the
ZCT at the position of the continuous line in the
drawing, then the primary conductor of the ZCT
forms a loop. To avoid this, the ZCT must be
placed at the position shown by the dotted line
in the drawing.
Induction can also be generated in the input circuit of the earth leakage relay, and it is necessary to braid the lead wires between the earth
leakage relay, and the ZCT.
ELCB
1.2×50µS
A
ELCB
11A
B
ELCB
1A
10A
Load
9A
10A
20A
Parallel circuits
M
ZCT
ZCT
Common earth wire
Steel
base
Ground fault detection by earth wire
82
(7) Operation by wrong wire connection
Failure in passing the neutral wire through the ZCT
for the lines of single phase 3-wire or 3 phase 4wire is a simple mistake. In this case, the ELCB is
operated by single phase load current.
ZCT
Load
Wrong wire connection of 3 phase 4-wire line
On the other hand, the common earth wire shall
not go through the ZCT as it can be cause malfunction at leakage.
M
ZCT
Common earth wire
Wrong connection of common earth wire
(8) Operation by inadequate earth
Though the wire is grounded at the earth side,
the wire shall not be earthed at the load side. By
the voltage of voltage drop in the line at the earth
side, a part of the load current is diverted as
shown by I’T, and the ELCB is operated.
M
IT
I'T
Inadequate double ground
(9) Operation of sound circuit at ground fault of shunt circuit
Not only the ELCB in the ground fault circuit but also the one in the sound circuit is operated in some cases
through the circuit as illustrated below. This can be avoided by keeping sensitive current suitably for the leak
current by static capacity to ground.
Fault circuit
Sound circuit
Operation of sound circuit by static capacity to ground
(10) Operation by overload and short-circuit
It is natural that the devices having overload or short-circuit operation elements operate at short-circuit. However, ELCB is commonly
used for many other purposes, and it tends to be overlooked that ELCB operate even at an overload and a short-circuit failure.
Moreover, even the one dedicated to ground fault is sometimes operated by an excessive overload and short-circuit because
balance performance of ELCB is limited. In these cases, however, overload and short-circuit can be noticed if they are significant.
(11) Environment of vibration, impact, high temperature etc.
These factors may be taken almost equal to those of Mitsubishi’s MCCB. Heat resistivity of electronic circuits tends to be fell
unreliable. To Mitsubishi’s ELCB, enough allowance is given to ratings of the parts, the parts which can withstand high temperature operation are used, and the ICs incorporating tempereture compensation circuits are used to ensure stable operation even
in varying temperature environment.
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(12) Operation by carrier phone unit
Malfunctions of the ELCB can result in some cases when attached to a line provided with a carrier
phone, which enables calls through the power line.
Since the carrier phone forcefully gives high frequency signals (normally 50kHz to 400kHz) between
the line and the ground, the ELCB detects the high frequency signals as if they are leak current and
leads to malfunction. Malfunction or not depends largely on magnitude of the high frequency signals,
high frequency characteristic of the ELCB, and degree of rated sensitive current.
(13) Operation by electromagnetic wave
When a portable type transceiver is placed near the ELCB at transmission, particularly intense magnetic field is generated easily resulting in malfunction. Generally speaking, frequency bands of portable type transceivers are 27/28MHz, 50/50MHz, 150MHz, 400MHz, and 900MHz, and the output is
about 0.5 to 5W. It is confirmed that the ELCB is free from any malfunction when different kinds of
transceivers of 5W output are used for transmission being placed at 1m from the ELCB.
(14) Operation by inverters
Inverters operate many high-frequency components as they turn A.C. power supply to D.C. through
rectification, then turn to A.C. again by switching through transistors.
Increased static capacity to ground sometimes causes malfunctions as the high frequency components are kept flowing by the static capacity to ground. To use ELCB in general in an inverter circuit, it
is necessary to select those of lower sensitive current than usual in order avoid unnecessary operation.
For ground fault detection of high sensitivity in inverter circuit and yet for stable ground fault detection
at both the primary and the secondary sides of the inverters, it is necessary to use an ELCB designed
for higher harmonic earth-leakages and surges, which is hardly affected by high frequency components, as the measure against the inverter.
It is also essential to install the ELCB at the primary side of the inverter, and never at the secondary
side.
Inverter
ELCB
1C1
IM
1C2
Applicable circuit to inverter
(15) Others
A load equipment is protected by a surge absorber
As electronic arrangement of load equipSurge
ment advances, surge absorbers are inLoad
equipment
stalled in the equipment more and more to
ELCB
Circuit and
protect them against surge. As the surge abroute of leak
Load
sorbers connected to the ground discharge
IS
current to
equipment
ground
the surge to the ground, a high leak current
Discherge gap
type absorber
is generated to the ground, for a short time
IS
though, and unnecessary operation of the
Gapless surge
absorber
ELCB is resulted in some cases.
Most Mitsubishi’s ELCB are provided with a
Leak current to ground through surge absorber
DPDC surge discriminating circuit for judging ground fault current by failure such as faulty insulation from leak current to ground by surge, and
improvement in the performance of preventing unnecessary operation is realized even when the surge
absorber is installed between the line and the ground.
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